Every touch screen phone uses a similar method, but what makes the iPhone unique is how the iPhone OS responds so quickly to swipes, pinches, and finger presses -- so fast that there is a burgeoning market for high-quality iPhone games that some say rival even the mighty Nintendo DS and PlayStation Portable.
Proximity Sensor Blanks Screen Automatically
When you move the iPhone to your ear, it automatically blanks the screen. This saves battery power, since you don't need the screen while talking on the phone (normally), and it also prevents you from touching an onscreen key -- such as the one to end a call -- by mistake.
Based on our own hands-on testing with the device, there are at least two (and possibly three) infrared sensors located near the ear speaker. Like most proximity sensors in smartphones, the iPhone sends out an electromagnetic field that scans for obstructions in an area about a half-inch away from the phone. Test this by placing an object over one of the sensors. The screen will go blank, and then reappear when you move the object away.
The tilt feature, or accelerometer, changes orientation in e-mail, the browser and other apps, and comes in handy in games such as Heavy Mach., where you can tilt the iPhone to move a tank left or right.
Jon Peddie, a consumer tech analyst, explains how the accelerometer works. "The accelerometer knows where the center of the earth is," Peddie says. "The trick is to sense a change."
Peddie explains that the first accelerometers had tiny magnetic cylinders that could slide from inside one very tightly wound transformer to another nearby, causing the signal in one to go down while the signal in the other went up. These were called linear voltage displacement transducers.
Today, like everything else electronic, the iPhone employs micro-electromechanical systems (MEMS). These devices have tiny (3 microns thick and 125 to 150 microns long) polysilicon arms with small hammer-like blocks on the end. They act like springs and hold the MEMS structure above a substrate. Acceleration causes the arms to deflect from their center position. And just like in the old electro-mechanical devices, the movement of that tiny mass is detected, by capacitors in this case, and a signal is generated.
iPhone's Tilt Feature
The tilt feature in some games uses the iPhone accelerometer, which changes direction in relation to the center of the earth.
When you shake the iPhone while listening to music, you will hear a random song -- either from the artist who's currently playing or from the playlist. Some apps, such as the Daylite Touch business productivity manager, use the shake feature to sync data. But you have to give the iPhone a good, firm shake to convince the application that you really want to sync up.
What we know from hands-on testing is that the iPhone shake feature uses the accelerometer. When it senses the phone has moved (in this case, from side to side), the OS triggers an API call for syncing or a random song. The accelerometer is sensitive enough, says Peddie, to know the difference between a shake and just turning the phone to its side to signal landscape mode.
Global Positioning System Finds Your Current Location
As long as you are outside and not stuck in a tunnel or inside an office complex, your iPhone can find your exact location using an internal GPS. Like most devices and smartphones with built-in GPS, the receiver in the iPhone can read a signal from a series of orbiting satellites -- about three dozen of them -- that transmit a near-constant signal.
The iPhone receiver reads data from the satellites and figures out -- based on how long the transmission takes -- the distance to the satellites, and then calculates your location. When the GPS receives another GPS signal, it more accurately determines your location. Once the iPhone acquires three satellite signals, the receiver triangulates your position.